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Providing evidence to improve practice

Individual study: Release of captive-bred female mallards Anas platyrhynchos leads to very low return rates in wetlands in Canada

Published source details

Yerkes T. & Bluhm C. (1998) Return Rates and Reproductive Output of Captive-Reared Female Mallards. The Journal of Wildlife Management, 62, 192-198


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Release captive-bred individuals into the wild to restore or augment wild populations of wildfowl Bird Conservation

A replicated, controlled study in wetlands in southwest Manitoba, Canada, between 1992 and 1995 (Yerkes & Bluhm 1998) found that only 2-3% of 1,766 released captive-bred female mallards Anas platyrhynchos were re-sited close to the release site (36 females positively identified and 19 more possibly identified). Annual rates ranged from nearly 10% of 1992 releases to only 1% of 1994 releases being seen again. If these numbers are adjusted for an average mortality of 60% for juvenile females, return rates were still only 6-9%. Comparisons of reproductive success were difficult due to small sample sizes (12 captive-reared females and 30 wild females were monitored): with 60% of wild females and either 71% (1993) or 0% (1994) of captive-reared females nesting. Nest success was 80% for five captive-reared females; it ranged from 11% (1993) to 67% (1994) for wild females, dependent on whether the majority nested on the ground or on artificial structures. Releases involved acclimatising groups of ducklings for 6-10 hours in open-topped cages before allowing them out. Supplementary food was also provided for three weeks after release (see ‘Provide supplementary after release’ for more information on this release technique).